Intermediate Mn Research Articles

Local polarization in oxygen-deficient LaMnO3 induced by charge localization in the Jahn-Teller distorted structure

The functional properties of transition metal perovskite oxides are known to result from a complex interplay of magnetism, polarization, strain, and stoichiometry. Here, we show that for materials with a cooperative Jahn-Teller distortion, such as LaMnO$_3$ (LMO), the orbital order can also couple to the defect chemistry and induce novel material properties. At low temperatures, LMO exhibits a strong Jahn-Teller distortion that splits the $e_g$ orbitals of the high-spin Mn$^{3+}$ ions and leads to alternating long, short, and intermediate Mn--O bonds. Our DFT+$U$ calculations show that, as a result of this orbital order, the charge localization in LMO upon oxygen vacancy formation differs from other manganites, like SrMnO$_3$, where the two extra electrons reduce the two Mn sites adjacent to the vacancy. In LMO, relaxations around the defect depend on which type of Mn--O bond is broken, affecting the $d$-orbital energies and leading to asymmetric and hence polar excess-electron localization with respect to the vacancy. Moreover, we show that the Mn--O bond lengths, orbital order and consequently the charge localization and polarity are tunable via strain.

Nitric Oxide Dioxygenation by O2 Adducts of Manganese Porphyrins.

We describe here nitric oxide dioxygenation (NOD) by the dioxygen manganese porphyrin adducts Mn(Por)(η2-O2) (Por2- = the meso-tetra-phenyl or meso-tetra-p-tolylporphyrinato dianions, TPP2- and TTP2-). The Mn(Por)(η2-O2) was assembled by adding O2 to sublimed layers of MnII(Por). When NO was introduced and the temperature was slowly raised from 80 to 120 K, new IR bands with correlated intensities grew concomitant with depletion of the υ(O2) band. Isotope labeling experiments with 18O2, 15NO, and N18O combined with DFT calculations provide the basis for identifying the initial intermediates as the six-coordinate peroxynitrito complexes (ON)Mn(Por)(η1-OONO). Further warming to room temperature led to formation of the nitrato complexes Mn(Por)(η1-ONO2), thereby demonstrating the ability of these metal centers to promote NOD. However, comparable quantities of the nitrito complexes Mn(Por)(η1-ONO) are also formed. In contrast, when the analogous reactions were initiated with the weak σ-donor ligand tetrahydrofuran or dimethyl sulfide present in the layers, formation of Mn(Por)(η1-ONO2) is strongly favored (∼90%). The latter are formed via a 6-coordinate intermediate (L)Mn(Por)(η1-ONO2) (L = THF or DMS) that loses L upon warming. These reaction patterns are compared to those observed previously with analogous iron and cobalt porphyrin complexes.

Electrochemical Behaviors of MnO2 on Lead Alloy Anode during Pulse Electrodeposition for Efficient Manganese Electrowinning

The electrochemical performances of deposited MnO2 on lead alloy anode by pulse current (PC) and direct current (DC) electrodeposition in manganese sulfate solution were investigated by performing measurements of galvanostatic polarization, cyclic voltammetry (CV), and Tafel tests. The composition and morphology of MnO2 were observed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The anode deposited with MnO2 layers by PC electrodeposition presented a lower anodic potential of 60 mV and more uniform potential oscillating attractor with fractal dimension of 1.0337 compared with those of DC electrodeposition. In addition, MnO2 layers exhibited excellent corrosion resistance because less intermediate oxide Mn(III) appeared in anode deposits. Furthermore, the cathodic current efficiency improved by 3.11∼3.77% and energy consumption decreased by 5.30∼8.17% after galvanostatic electrolysis for 2∼8 h by using PC instead of DC for manganese metal electrodeposition. As an external control method, PC electrodeposition not only regulated the structure and surface morphology of MnO2 but also affected the anode electrochemical behaviors and cathode manganese metal deposition. Electrochemical oscillations and other characteristics of anode reaction described in this study could inspire future work on promoting the whole electrowinning process.

Toward Combined Carbon Capture and Recycling: Addition of an Amine Alters Product Selectivity from CO to Formic Acid in Manganese Catalyzed Reduction of CO2.

Owing to the energetic cost associated with CO2 release in carbon capture (CC), the combination of carbon capture and recycling (CCR) is an emerging area of research. In this approach, "captured CO2," typically generated by addition of amines, serves as a substrate for subsequent reduction. Herein, we report that the reduction of CO2 in the presence of morpholine (generating mixtures of the corresponding carbamate and carbamic acid) with a well-established Mn electrocatalyst changes the product selectivity from CO to H2 and formate. The change in selectivity is attributed to in situ generation of the morpholinium carbamic acid, which is sufficiently acidic to protonate the reduced Mn species and generate an intermediate Mn hydride. Thermodynamic studies indicate that the hydride is not sufficiently hydritic to reduce CO2 to formate, unless the apparent hydricity, which encompasses formate binding to the Mn, is considered. Increasing steric bulk around the Mn shuts down rapid homolytic H2 evolution rendering the intermediate Mn hydride more stable; subsequent CO2 insertion appears to be faster than heterolytic H2 production. A comprehensive mechanistic scheme is proposed that illustrates how thermodynamic analysis can provide further insight. Relevant to a range of hydrogenations and reductions is the modulation of the hydricity with substrate binding that makes the reaction favorable. Significantly, this work illustrates a new role for amines in CO2 reduction: changing the product selectivity; this is pertinent more broadly to advancing CCR.

Activation of MnFe2O4 by sulfite for fast and efficient removal of arsenic(III) at circumneutral pH: Involvement of Mn(III)

As(III) oxidation to As(V) is deemed necessary for better arsenic removal, and separation is still the optimal approach for water remediation from As(III). Herein, sulfite (SIV) was adopted to activate MnFe2O4 for simultaneous oxidation and adsorption of As(III) in neutral water. The As(III) removal was more efficient than a peroxidation of As(III) followed by adsorption. The adsorption capacity of MnFe2O4/S(IV) for As(III) (26.257 mg g−1) was much higher than those of MnFe2O4 alone for As(III) (9.491 mg g−1) and As(V) (9.142 mg g−1). The mechanistic study corroborated that intermediate Mn(III) was the dominant oxidant responsible for rapid oxidation of As(III), and the dual roles of S(IV) as a complexing ligand and a precursor of oxysulfur radicals accelerated the redox cycle of Mn(II)/Mn(III). Moreover, S(IV) enhanced arsenic adsorption by driving more production of monodentate complexes. As(III) can be effectively removed over a wide range of temperatures (283.15–313.15 K) and pH (3–10) with the optimal pH of 7. The effect of coexisting ions and reusability of MnFe2O4 were also investigated. Especially, the superior performance of MnFe2O4/S(IV) for As(III) removal in various water matrixes may help develop new removal technologies based on active Mn(III) for the water decontamination from As(III).

Facile synthesis of Mn-doped BiOCl for metronidazole photodegradation: Optimization, degradation pathway, and mechanism

Manganese-doped bismuth oxychloride (Mn-BiOCl) photocatalysts were facilely synthesized for the photodegradation of metronidazole (MTZ), and the as-prepared Mn-BiOCl was systematically characterized. The results show that the introduction of Mn2+ to BiOCl increases its MTZ removal efficiency through increasing its specific surface area, broadening its light absorption region, and facilitating photoinduced carrier separation. The enhancement of the optical properties is ascribed to the generation of an intermediate Mn 3p-O 2d energy level in the forbidden gap of Mn-BiOCl based on the density functional theory calculations. Mn-BiOCl also exhibited favorable stability and recyclability after four cycles. Moreover, the results of the quenching experiments indicate that superoxide radicals (O2−), hydroxyl radicals (OH) and holes (h+) participated in MTZ degradation over Mn-BiOCl, and the electron spin resonance (ESR) test demonstrated that more OH was generated in the Mn-BiOCl process than the BiOCl process. This was explained by the H2O adsorption energy and bond parameter on the photocatalyst’s surface. Finally, the photodegradation pathway of MTZ was elaborated based on the intermediate analysis, and a mechanism for the promotion of MTZ photodegradation through Mn-doping BiOCl was proposed.

Coupled As and Mn Redox Transformations in an Fe(0) Electrocoagulation System: Competition for Reactive Oxidants and Sorption Sites.

Iron electrocoagulation (EC) can be used for the decentralized treatment of arsenic(As)-contaminated groundwater. Iron EC involves the electrolytic dissolution of an Fe(0) electrode to Fe(II). This process produces reactive oxidants, which oxidize As(III) and Fe(II) to As(V) and a range of Fe(III) (oxyhydr)oxide phases. Here, we investigated the impact of manganese (Mn) on As removal, since the two often co-occur in groundwater. In the absence of Mn(II), we observed rapid As(III) oxidation and the formation of As(V)-Fe(III) polymers. Arsenic removal was achieved upon aggregation of the As(V)-Fe(III) polymers. In the presence of Mn, the mechanism of As removal varied with pH. At pH 4.5, As(III) was oxidized rapidly by OH• and the aggregation of the resulting As(V)-Fe(III) polymers was enhanced by the presence of Mn. At pH 8.5, As(III) and Mn(II) competed for Fe(IV), which led As(III) to persist in solution. The As(V) that did form was incorporated into a mixture of As(V)-Fe(III) polymers and a ferrihydrite-like phase that incorporated 8% Mn(III); some As(III) was also sorbed by these phases. At intermediate pH values, As(III) and Mn(II) also competed for the oxidants, but Mn(III) behaved as a reactive intermediate that reacted with Fe(II) or As(III). This result can explain the presence of As(V) in the solid phase. This detailed understanding of the As removal mechanisms in the presence of Mn can be used to tune the operating conditions of Fe EC for As removal under typical groundwater conditions.

Role of pyrophosphate on the degradation of sulfamethoxazole by permanganate combined with different reductants: Positive or negative.

Activating permanganate with reductants has gained increasing attention recently for efficient organic contaminants abatement via reactive intermediate Mn species. However, few studies have been conducted to explore the role of pyrophosphate (PP), a typical complexing agent for intermediate Mn species, in activated permanganate systems. In this study, taking sulfamethoxazole (SMX) as a probe compound, the influences of PP on SMX degradation by permanganate/thiosulfate and permanganate/hydroxylamine were extensively studied. It was found that both thiosulfate and hydroxylamine were able to activate permanganate for oxidation of SMX in the absence of PP. However, upon the introduction of PP, opposite effects were observed in the two systems where PP further improved the activation of permanganate by thiosulfate but dampened the performance of permanganate/hydroxylamine markedly. For permanganate/hydroxylamine system, MnO2 was determined to be the only reactive oxidative species accounting for SMX degradation in the absence of PP, and its generation could be completely inhibited by PP. While in permanganate/thiosulfate system, both Mn(V) and MnO2 were responsible for SMX oxidation, and the introduction of PP could strengthen the oxidative ability of Mn(V). These results could shed some insights on the suitability of applying PP to explore the kinetics and mechanisms of manganese involved redox reactions. PRACTITIONER POINTS: Both Na2 S2 O3 and NH2 OH·HCl can activate KMnO4 for SMX removal without PP. MnO2 is the reactive oxidative species involved in KMnO4 /NH2 OH·HCl system. Mn(V) and MnO2 account for the SMX oxidation by KMnO4 /Na2 S2 O3 system. PP could inhibit the formation of MnO2 but enhance the oxidative ability of Mn(V).

Effect of Mn doping on the low-temperature synthesis of tricalcium phosphate (TCP) polymorphs

Effect of Mn doping on the low-temperature synthesis of tricalcium phosphate (TCP) polymorphs was demonstrated in α- and β-TCP polymorphs prepared by wet precipitation method under identical conditions and annealed at 700 °C. Calcium phosphates with Mn doping level in the range from 1 to 5 mol% were studied and the formation of desired polymorph was controlled by varying Mn content in as-prepared precipitates. It was found that increasing Mn content resulted in the formation of β-TCP, while α-TCP was obtained with low Mn doping level, whereas a mixture of two polymorphs was obtained for intermediate Mn concentrations. Moreover, doping with Mn ions allowed the synthesis of β-TCP at relatively low temperature (700 °C). Synthesized compounds were characterized by X-ray diffraction (XRD) analysis, electron paramagnetic resonance (EPR), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), inductively coupled plasma optical emission spectrometry (ICP-OES) and colorimetric MTT assay.

Biogenic and Synthetic MnO2 Nanoparticles: Size and Growth Probed with Absorption and Raman Spectroscopies and Dynamic Light Scattering

MnO2 nanoparticles, similar to those found in soils and sediments, have been characterized via their UV-visible and Raman spectra, combined with dynamic light scattering and reactivity measurements. Synthetic colloids were prepared by thiosulfate reduction of permanganate, their sizes controlled with adsorbates acting as capping agents: bicarbonate, phosphate, and pyrophosphate. Biogenic colloids, products of the manganese oxidase, Mnx, were similarly characterized. The band-gap energies of the colloids were found to increase with decreasing hydrodynamic diameter, Dh, and were proportional to 1/ Dh2, as predicted from quantum confinement theory. The intensity ratio of the two prominent Mn-O stretching Raman bands also varied with particle size, consistent with the ratio of edge to bulk Mn atoms. Reactivity of the synthetic colloids toward reduction by Mn2+, in the presence of pyrophosphate to trap the Mn3+ product, was proportional to the surface to volume ratio, but showed surprising complexity. There was also a remnant unreactive fraction, likely attributable to Mn(III)-induced surface passivation. The band gap was similar for biogenic and synthetic colloids of similar size, but decreased when the enzyme solution contained pyrophosphate, which traps the intermediate Mn(III) and slows MnO2 growth. The band gap/size correlation was used to analyze the growth of the enzymatically produced MnO2 oxides.

Trivalent manganese on vacancies triggers rapid transformation of layered to tunneled manganese oxides (TMOs): Implications for occurrence of TMOs in low-temperature environment

Tunneled Mn oxides (TMOs) are common minerals in natural environment, particularly in ferromanganese nodules of oceanic and lake sediments. Their structures host a considerable amount of transition and rare earth metals, thus mediating metal cycling and bearing potential economic interest for exploiting these metals. TMOs form through topotactic transformation of layered Mn oxides (LMOs), such as vernadite, in natural environment. Trivalent Mn (Mn(III)) in the LMO structure is a critical player in the transformation, and the transformation is believed to be extremely slow at room temperature. However, the specific role of Mn(III) and its impacts on the transformation kinetics remain unknown.In the present study, we show that the formation of Mn(III) on vacancies of an LMO is the initial transformation step leading to TMOs, and that the transformation can be rapid at room temperature and circumneutral pH. Specifically, after pre-adsorbed with Mn(II) on vacancies at pH 4, δ-MnO2, a hexagonal birnessite analogous to vernadite, starts to transform to a 4 × 4 TMO at 1 h upon incubation at pH 7 and 21 °C under anoxic conditions. The rapid transformation is triggered by the comproportionation reaction between the vacancy-adsorbed Mn(II) and Mn(IV) in δ-MnO2 that produces Mn(III) on the vacancies. Such intermediate Mn(III)-rich product acts as a precursor for subsequent rapid structural rearrangement to form tunnels. An incubation at lower or higher pH retards the transformation due to an insufficient amount of Mn(III) (pH 6) or the formation of triclinic birnessite (pH 8) as an intermediate product. The presence of O2 favors the formation of triclinic birnessite at pH 8 and thus retards the transformation whereas O2 enhances production of Mn(III)-rich hexagonal birnessite at pH 6 and 7 and promotes the transformation. We propose a novel transformation mechanism of LMOs to TMOs, highlighting the role of vacancy-adsorbed Mn(III) in the transformation. This work changes our understanding of TMO formation kinetics and suggests TMOs can readily form in low-temperature redox-fluctuating environment, such as lake and oceanic sediments where Mn(II) often coexists with LMOs.

Multivalent Presentation of Peptide Targeting Groups Alters Polymer Biodistribution to Target Tissues.

Drug delivery to bone is challenging, whereby drug distribution is commonly <1% of injected dose, despite development of several bone-targeted drug delivery systems specific to hydroxyapatite. These bone-targeted drug delivery systems still suffer from poor target cell localization within bone, as at any given time overall bone volume is far greater than acutely remodeling bone volume, which harbors relevant cell targets (osteoclasts or osteoblasts). Thus, there exists a need to target bone-acting drugs specifically to sites of bone remodeling. To address this need, this study synthesized oligo(ethylene glycol) copolymers based on a peptide with high affinity to tartrate-resistant acid phosphatase (TRAP), an enzyme deposited by osteoclasts during the bone resorption phase of bone remodeling, which provides greater specificity relevant for bone cell drugging. Gradient and random peptide orientations, as well as polymer molecular weights, were investigated. TRAP-targeted, high molecular weight (Mn) random copolymers exhibited superior accumulation in remodeling bone, where fracture accumulation was observed for at least 1 week and accounted for 14% of tissue distribution. Intermediate and low Mn random copolymer accumulation was lower, indicating residence time depends on Mn. High Mn gradient polymers were cleared, with only 2% persisting at fractures after 1 week, suggesting TRAP binding depends on peptide density. Peptide density and Mn are easily modified in this versatile targeting platform, which can be applied to a range of bone drug delivery applications.

Systematic comparison of single-walled carbon nanotube/poly(vinyl acetate) graft-to reactions

The covalent grafting of polymers to single-walled carbon nanotubes (SWCNTs) is widely used to improve solvent compatibility, as well as composite and functional performance. Here, three different graft-to strategies are directly compared, using azide, diazonium, and bromide terminated polymers, over four different molecular weights (oligomeric to 10 kDa) using specifically synthesized low polydispersity, end-group controlled poly(vinyl acetate) (PVAc) prepared by polymerisation using a bespoke protected-amine RAFT agent. Coupling of the bromo-polymer to reduced SWCNTs led to higher degrees of functionalisation (grafting ratios up to 68.9%) than the azide and diazonium grafting reactions, attributed to better initial dispersion of the pre-grafted SWCNTs. The use of higher molecular weight polymers led to a decrease in the total weight of polymer grafted, as the increase in per-polymer weight is more than offset by steric occlusion on the SWCNT surface. For these graft-to reactions, the dispersibility of grafted SWCNTs was found to depend most strongly on the polymer molecular weight, not total weight of grafted polymer or grafting chemistry, with an intermediate Mn∼5757 PVAc giving the best dispersibilities, at up to 118 mg L−1.

Efficient catalytic As(III) oxidation on the surface of ferrihydrite in the presence of aqueous Mn(II)

Arsenic is a carcinogenic element that exists primarily as arsenate [As(V)] and arsenite [As(III)] in the nature environment, with As(III) being more toxic and mobile of the two species. In addition, ferrihydrite, which is widely distributed in soils and aquatic environments, can catalyze the oxidation of Mn(II) and accelerate the formation of high-valence Mn, which can significantly influence the speciation, toxicity, and mobility of As when these species co-exist. In this context, we herein explored the mechanism of As(III) oxidation in the presence of ferrihydrite and Mn(II) using a kinetic approach combined with multiple spectroscopic techniques, including X-ray absorption near edge spectroscopy, in situ horizontal attenuated total-reflectance Fourier transform infrared spectroscopy, and in situ quick scanning X-ray absorption spectroscopy. Our results indicate that efficient As(III) oxidation by dissolved O2 occurs on the surface of ferrihydrite in the presence of aqueous Mn(II). Compared with As(III) oxidation in the presence of ferrihydrite and Mn oxides (i.e., Mn oxides/hydroxides), the degree of As(III) oxidation in the ferrihydrite-Mn(II) system was significantly higher, and the majority of generated As(V) was adsorbed on the mineral (i.e., ferrihydrite) surface. Furthermore, As(III) oxidation was enhanced upon increasing both the molar ratio of Mn(II)/As(III) and the solution pH. The greater As(III) oxidation by O2 in the ferrihydrite-Mn(II) system was mainly attributed to the formation of a strong oxidant of the instantaneous intermediate Mn(III) species via Mn(II) oxidation under catalysis by the ferrihydrite surface. Moreover, As(III) oxidation occurred mainly on the ferrihydrite surface and was accompanied by the regeneration of Mn(II), thereby rendering it recyclable. These results therefore provide new insights into the mechanism of As(III) oxidation on the surfaces of Fe oxides (i.e., Fe oxides/hydroxides) in the presence of aqueous Mn(II) as well as the new details regarding the electron transfer mechanisms between the As(III)-Mn(II, III)-O2 species at the ferrihydrite surface, and could lead to novel approaches for As(III) contaminant remediation in the environment.

Enhancement in magnetocaloric properties of NiMnGa alloy through stoichiometric tuned phase transformation and magneto-thermal transitions

The investigation is focussed on phase generation and magnetocaloric properties of a series of Ni77-XMnXGa23 (x=22, 23, 24, 25, 27) alloys prepared through arc melting furnace. With increase in Mn content, the alloys showed systematic transition from a non-modulated martensite (NM) to a fully austenitic parent phase through an appearance and coexistence of modulated (M) structure. Intermediate Mn containing alloy (#Mn24) not only displayed high magnetic entropy change (ΔSM) of −7.7J/kg−1K−1 but also large Refrigerant Capacity (RC) of 169J.Kg−1 at magnetic field change of 3 T compared to other alloys. The coexisting martensite (NM, M) and parent austenite as well as overlapping thermomagnetic and structural transformation was deliverable through tuning of alloy chemistry wherein Ni was systematically substituted by Mn. Transmission electron microscopy (TEM) supported the proposition with existence of martensite plates of different morphology in Mn24 alloy exhibiting superior magnetocaloric properties.

NiMo catalysts supported on Mn-Al2O3 for dibenzothiophene hydrodesulfurization application

Modification of the traditional Al2O3 support through addition of manganese to Al2O3 mixed Mn-Al oxides was herein envisaged to obtain highly active NiMo catalysts for hydrodesulfurization application. The effect of adding manganese was determined considering different Mn-Al2O3 supports synthetized using a sol–gel approach. The manganese-containing supports were furthermore impregnated with Ni(NO3)2+(NH4)6Mo7O24 aqueous solutions at pH=9 and characterized at their oxide state using UV–vis diffuse reflectance and Raman spectroscopies after drying and calcination steps. NiMo/Mn-Al2O3 catalysts were also characterized at the sulfide state mainly by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Finally, the sulfide catalysts were evaluated in the hydrodesulfurization of dibenzothiophene.Results show that the oxidation state of manganese species directly influences the nature of the Mo oxide species and their interaction with the Al2O3 support. At low Mn content (up to 0.5mol% Mn as MnO), Mn2+ species leads to weaker interaction with the support and a higher intrinsic activity of the NiMoS species. However, these promoted sites are also formed in a lower amount than without adding Mn to the support. At too high manganese content (≥2mol% Mn as MnO), Mn3+ species are formed and react with Ni to form a spinel phase decreasing the proportion of promoted phase to be formed after sulfidation. The highest activity is therefore observed at an intermediate Mn content of 1mol% for which a higher intrinsic activity resulting from weaker support interaction and higher sulfidation rate combine together to achieve highly active NiMo HDS catalysts.

Electrochemical Reduction of Oxygen in Aprotic Ionic Liquids Containing Metal Cations: A Case Study on the Na-O2 system.

Metal-air batteries are intensively studied because of their high theoretical energy-storage capability. However, the fundamental science of electrodes, electrolytes, and reaction products still needs to be better understood. In this work, the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) was chosen to study the influence of a wide range of metal cations (Mn+ ) on the electrochemical behavior of oxygen. The relevance of the theory of Lewis hard and soft acids and bases to predict satisfactorily the reduction potential of oxygen in electrolytes containing metal cations is demonstrated. Systems with soft and intermediate Mn+ acidity are shown to facilitate oxygen reduction and metal oxide formation, whereas oxygen reduction is hampered by hard acid cations such as sodium and lithium. Furthermore, DFT calculations on the energy of formation of the resulting metal oxides rationalize the effect of Mn+ on oxygen reduction. A case study on the Na-O2 system is described in detail. Among other things, the Na+ concentration of the electrolyte is shown to control the electrochemical pathway (solution precipitation vs. surface deposition) by which the discharge product grows. All in all, fundamental insights for the design of advanced electrolytes for metal-air batteries, and Na-air batteries in particular, are provided.

Role of magnetic dopants in the phase diagram of Sm 1111 pnictides: The case of Mn

The deliberate insertion of magnetic Mn dopants in the Fe sites of the optimally-doped SmFeAsO0.88-F0.12 iron-based superconductor can modify in a controlled way its electronic properties. The resulting phase diagram was investigated across a wide range of manganese contents (x) by means of muon-spin spectroscopy (muSR), both in zero- and in transverse fields, respectively, to probe the magnetic and the superconducting order. The pure superconducting phase (at x < 0.03) is replaced by a crossover region at intermediate Mn values (0.03 =< x < 0.08), where superconductivity coexists with static magnetic order. After completely suppressing superconductivity for x = 0.08, a further increase in Mn content reinforces the natural tendency towards antiferromagnetic correlations among the magnetic Mn ions. The sharp drop of Tc and the induced magnetic order in the presence of magnetic disorder/dopants, such as Mn, are both consistent with a recent theoretical model of unconventional superconductors [M. Gastiasoro et al., ArXiv 1606.09495], which includes correlation-enhanced RKKY-couplings between the impurity moments.

Small but mighty: how minor components drive major biogeochemical cycles.

Small but mighty: how minor components drive major biogeochemical cycles.

RNA-Seq analysis uncovers non-coding small RNA system of Mycobacterium neoaurum in the metabolism of sterols to accumulate steroid intermediates.

BackgroundUnderstanding the metabolic mechanism of sterols to produce valuable steroid intermediates in mycobacterium by a noncoding small RNA (sRNA) view is still limited. In the work, RNA-seq was implemented to investigate the noncoding transcriptome of Mycobacterium neoaurum (Mn) in the transformation process of sterols to valuable steroid intermediates, including 9α-hydroxy-4-androstene-3,17-dione (9OHAD), 1,4-androstadiene-3,17-dione (ADD), and 22-hydroxy-23, 24-bisnorchola-1,4-dien-3-one (1,4-BNA).ResultsA total of 263 sRNA candidates were predicted from the intergenic regions in Mn. Differential expression of sRNA candidates was explored in the wide type Mn with vs without sterol addition, and the steroid intermediate producing Mn strains vs wide type Mn with sterol addition, respectively. Generally, sRNA candidates were differentially expressed in various strains, but there were still some shared candidates with outstandingly upregulated or downregulated expression in these steroid producing strains. Accordingly, four regulatory networks were constructed to reveal the direct and/or indirect interactions between sRNA candidates and their target genes in four groups, including wide type Mn with vs without sterol addition, 9OHAD, ADD, and BNA producing strains vs wide type Mn with sterol addition, respectively. Based on these constructed networks, several highly focused sRNA candidates were discovered to be prevalent in the networks, which showed comprehensive regulatory roles in various cellular processes, including lipid transport and metabolism, amino acid transport and metabolism, signal transduction, cell envelope biosynthesis and ATP synthesis. To explore the functional role of sRNA candidates in Mn cells, we manipulated the overexpression of candidates 131 and 138 in strain Mn-9OHAD, which led to enhanced production of 9OHAD from 1.5- to 2.3-fold during 6 d’ fermentation and a slight effect on growth rate.ConclusionsThis study revealed the complex and important regulatory roles of noncoding small RNAs in the metabolism of sterols to produce steroid intermediates in Mn, further analysis of which will promote the better understanding about the molecular metabolism of these sRNA candidates and open a broad range of opportunities in the field.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0462-2) contains supplementary material, which is available to authorized users.